Polyethylene terephthalate (PET), made by reacting terephthalic acid or dimethyl terephthalate and ethylene glycol, is a versatile thermoplastic polyester used in synthetic fibers, extruded films such as x-ray films, molded engineering components, and blow molded bottles. Worldwide production of PET is above 1,000,000 metric tons a year. With such enormous production, effective use of PET waste is desirable. Waste PET is readily available at costs as low as 35 cents per kilogram while its raw materials terephthalic acid and ethylene glycol cost 90 cents per kilogram and 40 cents per kilogram respectively.
PET waste can be repelletized and converted into extruded or molded articles. Alternatively, PET can be converted into low molecular weight oligomers by glycolysis using inexpensive ethylene glycol or diethylene glycol or expensive propylene glycol. Certain of these glycolysis products can be further reacted with an unsaturated acid or anhydride to make an unsaturated polyester resin which can be further reacted with large proportions of styrene to make a myriad of products. Unfortunately, as described by Vaidya and Nadkaini, in Industrial Engineering Chemical Research 1987, 26, 194-198; unsaturated polyester resins synthesized from ethylene glycol-based glycolyzed PET are incompatible with styrene monomer. However, Vaidya and Nadkaini found that PET waste depolymerized with expensive propylene glycol could be reacted with maleic anhydride and mixed with styrene monomer to produce useful unsaturated polyester resins. These resins were comparable in processability to conventional general purpose resin.
It would be economically advantageous if a process could be identified in which PET, glycolyzed using less costly glycols than propylene glycol, could effectively be used in producing styrenated, unsaturated polyester resins for commercial use. Any unsaturated polyester made using glycolyzed PET should be highly soluble in styrene so that manufacturers can use abundant proportions of styrene as they make articles. Some new approach is needed in order to solve the problem, described by Vaidya and Nadkaini, of the incompatibility with styrene monomer of unsaturated polyesters made using ethylene glycol based glycolyzed PET.